2023-06-21 08:43:22

by Pankaj Raghav

Subject: [RFC 1/4] fs: Allow fine-grained control of folio sizes

From: "Matthew Wilcox (Oracle)" <[email protected]>

Some filesystems want to be able to limit the maximum size of folios,
and some want to be able to ensure that folios are at least a certain
size. Add mapping_set_folio_orders() to allow this level of control
(although it is not yet honoured).

[Pankaj]: added mapping_min_folio_order()

Signed-off-by: Pankaj Raghav <[email protected]>
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
---
include/linux/pagemap.h | 46 +++++++++++++++++++++++++++++++++++++----
1 file changed, 42 insertions(+), 4 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 716953ee1ebd..462c36c9dd88 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -202,9 +202,15 @@ enum mapping_flags {
AS_EXITING = 4, /* final truncate in progress */
/* writeback related tags are not used */
AS_NO_WRITEBACK_TAGS = 5,
- AS_LARGE_FOLIO_SUPPORT = 6,
+ AS_FOLIO_ORDER_MIN = 8,
+ AS_FOLIO_ORDER_MAX = 13,
+ /* 8-17 are used for FOLIO_ORDER */
};

+#define AS_FOLIO_ORDER_MIN_MASK 0x00001f00
+#define AS_FOLIO_ORDER_MAX_MASK 0x0002e000
+#define AS_FOLIO_ORDER_MASK (AS_FOLIO_ORDER_MIN_MASK | AS_FOLIO_ORDER_MAX_MASK)
+
/**
* mapping_set_error - record a writeback error in the address_space
* @mapping: the mapping in which an error should be set
@@ -294,6 +300,29 @@ static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask)
m->gfp_mask = mask;
}

+/**
+ * mapping_set_folio_orders() - Set the range of folio sizes supported.
+ * @mapping: The file.
+ * @min: Minimum folio order (between 0-31 inclusive).
+ * @max: Maximum folio order (between 0-31 inclusive).
+ *
+ * The filesystem should call this function in its inode constructor to
+ * indicate which sizes of folio the VFS can use to cache the contents
+ * of the file. This should only be used if the filesystem needs special
+ * handling of folio sizes (ie there is something the core cannot know).
+ * Do not tune it based on, eg, i_size.
+ *
+ * Context: This should not be called while the inode is active as it
+ * is non-atomic.
+ */
+static inline void mapping_set_folio_orders(struct address_space *mapping,
+ unsigned int min, unsigned int max)
+{
+ mapping->flags = (mapping->flags & ~AS_FOLIO_ORDER_MASK) |
+ (min << AS_FOLIO_ORDER_MIN) |
+ (max << AS_FOLIO_ORDER_MAX);
+}
+
/**
* mapping_set_large_folios() - Indicate the file supports large folios.
* @mapping: The file.
@@ -307,7 +336,17 @@ static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask)
*/
static inline void mapping_set_large_folios(struct address_space *mapping)
{
- __set_bit(AS_LARGE_FOLIO_SUPPORT, &mapping->flags);
+ mapping_set_folio_orders(mapping, 0, 31);
+}
+
+static inline unsigned mapping_max_folio_order(struct address_space *mapping)
+{
+ return (mapping->flags & AS_FOLIO_ORDER_MAX_MASK) >> AS_FOLIO_ORDER_MAX;
+}
+
+static inline unsigned mapping_min_folio_order(struct address_space *mapping)
+{
+ return (mapping->flags & AS_FOLIO_ORDER_MIN_MASK) >> AS_FOLIO_ORDER_MIN;
}

/*
@@ -316,8 +355,7 @@ static inline void mapping_set_large_folios(struct address_space *mapping)
*/
static inline bool mapping_large_folio_support(struct address_space *mapping)
{
- return IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
- test_bit(AS_LARGE_FOLIO_SUPPORT, &mapping->flags);
+ return mapping_max_folio_order(mapping) > 0;
}

static inline int filemap_nr_thps(struct address_space *mapping)
--
2.39.2

2023-06-21 09:25:11

by Hannes Reinecke

Subject: Re: [RFC 1/4] fs: Allow fine-grained control of folio sizes

On 6/21/23 10:38, Pankaj Raghav wrote:
> From: "Matthew Wilcox (Oracle)" <[email protected]>
>
> Some filesystems want to be able to limit the maximum size of folios,
> and some want to be able to ensure that folios are at least a certain
> size. Add mapping_set_folio_orders() to allow this level of control
> (although it is not yet honoured).
>
> [Pankaj]: added mapping_min_folio_order()
>
> Signed-off-by: Pankaj Raghav <[email protected]>
> Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
> ---
> include/linux/pagemap.h | 46 +++++++++++++++++++++++++++++++++++++----
> 1 file changed, 42 insertions(+), 4 deletions(-)
>
Reviewed-by: Hannes Reinecke <[email protected]>

Cheers,

Hannes